For generic "white-label" DVRs, community-trusted sites like Unifore host various HiSilicon firmware versions (e.g., V4.02.R11).
Use a USB flash drive (8GB or smaller is often recommended) and format it to FAT32 . Download Firmware DVR HI3515 4CH 8MB rar
You can update either directly through the DVR interface or via a web browser: V4.02.R11 H.264/H.265 DVR/NVR Firmware Download For generic "white-label" DVRs